1. Field of the Invention
The present invention relates generally to cleaning of solid surfaces, such as semiconductor substrate, and, more particularly, to methods and apparatus for utilizing an external force to access solid-like characteristic of a liquid cleaning medium to clean a semiconductor substrate following fabrication processes.
2. Description of the Related Art
It is well-known in the art that there is a need to clean and dry a solid surface that has undergone a fabrication operation which leaves unwanted defects or contaminant particles on the solid surface. Examples of such fabrication operations include plasma etching (e.g., via etch or trench etch for copper dual damascene applications) and chemical mechanical polishing (CMP). Various cleaning processes have been used in removing the unwanted defects from the surface of the substrate after each fabrication operation. Some of the cleaning processes involve selecting a liquid medium with chemical structure that enables at least partial bonding or interaction with the particle contaminants and promptly removing the liquid medium along with the particle contaminants.
Still other processes involve selection of a liquid medium, substantially applying the liquid medium to cover at least a portion of the substrate, propagating acoustic energy through the liquid medium and using the acoustic energy to remove particles from the surface of the substrate. The propagation of acoustic energy through the liquid medium enables cleaning chiefly through cavitation, microstreaming, and chemical reaction enhancement when chemicals are used as the liquid medium. Cavitation is the rapid forming and collapsing of microscopic bubbles from dissolved gases in the liquid medium under the action of sonic agitation. Upon collapse, the bubbles release energy. The energy from the collapsed bubbles assists in particle removal through breakage of the various adhesion forces that allow the particles to adhere to the substrate. Acoustic microstreaming is the fluid motion induced by the velocity gradient from propagation of an acoustic wave through the liquid medium under a high frequency vibration. The acoustic energy provides the activation energy to facilitate the chemical reactions within the liquid medium.
As the critical dimensions of features formed on the surface of the substrate continue to decrease, the number of sub-micron particles with dimensions that are comparable to the critical dimensions of the features increases. Due to the critical dimensions of the sub-micron particles, there is always a need for improved cleaning techniques that substantially clean the surface of the substrate without damaging the features formed on the substrate so that the yield of devices resulting from the fabrication is not compromised.
It is in this context that embodiments of the invention arise.